The present invention is in the field of coal transportation and power plant utilization thereof and is specifically directed to unique methods and apparatus for conveying and feeding coal by a liquified gas/coal slurry pipeline to a power plant including unique power plant efficiency increasing methods and apparatus.
The vast majority of coal consumed at power plants in the United States is transported from the mine head to the power plants by rail or barge. Unfortunately, the cost of transportation by rail is quite substantial as a consequence of the inherent expense of rail transportation and the fact that individual railroads are frequently the only means by which coal can be transported from a particular mine. While barge transportation is generally more economical where available, many power plants and mines do not have access to waterways capable of enabling water transportation.
The foregoing and other problems have consequently resulted in a number of proposals for transporting coal in an liquid slurry pumped through a pipeline. A number of coal-water slurry pipelines have been built and commercially exploited in the United States with the longest pipeline of this type being in excess of 270 miles in length. However, coal-water slurry pipelines require both an adequate source of water conveniently located with respect to the mine and means for disposing of the transport water at the downstream end of the pipeline. Unfortunately, the foregoing circumstances are not always present, particularly in the West, and such pipelines are becoming less feasible with the passage of time.
The prior art has consequently come forth with a variety of proposals aimed at overcoming or reducing the shortcomings of present known coal transportation methods. For example, U.S. Pat. Nos. 4,173,530; 4,178,231; 4,178,233; and 4,265,737 disclose the concept of using fluorochlorocarbons as coal carriers in a slurry system. Bates U.S. Pat. No. 1,390,230 discloses the concept of a coal slurry in which the liquid carrier is oil or some other liquid hydrocarbon. Gruber, et al. U.S. Pat. No. 4,027,688 discloses a coal slurry in which pulverized coal is transported by a liquid hydrocarbon and methanol carrier mixture. Hamilton U.S. Pat. No. 1,385,447 discloses conveying coal through a pipeline by the use of a gas or fluid in which producer gas is a constituent of the carrier employed in the slurry. Keller U.S. Pat. No. 3,968,999 discloses the use of methanol or LPG as the slurry media. Wunsch, et al. U.S. Pat. No. 3,180,691 discloses the concept of providing a coal slurry in which the carrier media comprises a liquidifed gas maintained at a sufficient pressure to remain in liquified condition until released at the end of the pipeline for expansion to permit the carrier gas to separate from the solid materials. British Pat. No. 2,027,446 discloses the conveyance of pulverized coal with a liquid fuel constituent.
Other prior U.S. patents have disclosed the use of liquified carbon dioxide as the carrier media of a coal slurry system. For example, Paull U.S. Pat. No. 3,976,443 discloses a slurry tank 17 in which pulverized coal is mixed with liquid carbon dioxide and pumped through a pipeline by a feed pump 24 through a heater 26 for discharge in a burner 30.
Similarly, Santhanam U.S. Pat. Nos. 4,206,610 and 4,377,356 also discloses the concept of conveying coal by the use of a liquid carbon dioxide slurry.
However, none of the prior art patents suggesting the use of liquified carbon dioxide as the carrier media for a coal slurry has been commercially exploited in so far as Applicants are aware. One possible reason for the non-exploitation of the Santhanam patents is the fact that the specification and claims of at least the '610 patent conflictingly indicate that the coal/liquid carbon dioxide slurry is adiabatically expanded and that prior to the adiabatic expansion, heat is introduced into the slurry to make up for the heat lost in the expanding to avoid solidification of the carbon dioxide. Since adiabatic expansion by definition does not involve heat loss, the aforementioned patent presents a basic inconsistency on its face.
Thus, while a variety of coal slurry pipeline systems have been suggested, they have not effectively presented facts resulting in widespread acceptance.